Oxidation of vat and sulphur dyes



Patented Aug. 14,1945

. amass oxms'rroN or vs'r AND stamina ints George P. Vincent, Briarclifl Manor, N. Y., and Archie L. Dubeau, Bumiord, B. L, assignors to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation of Virginia No Drawing. Application February 4, 1943, Serial No. 474,716

Claims. (01.8-34) This invention relates to the dyeing of textile materials. It relates more particularly to im provements in the after-treatment following the impregnation of the textile material with the dyestuil'.

The invention is applicable generally to the treatment of cellulosic textiles, comprising either natural or artiilcialcellulosic fibers such as cotton, linen and regenerated cellulose, in the dyeing thereof with dyes, such as the so-called vat dyes and sulphur dyes, which require an afterthe color or improve the fastness thereof, or both.

The vat dyes, for instance, are normallyhighly insoluble in water and in their use they must'flrst be converted to a water-soluble form. The solubilization of these dyes is usually eflected by the use of a reducing agentsuch ashydrosul-phite in an alkali solution. The textile material to be dyed is impregnated with the solution of the reduced dye, generally designated a leuco solution,

and must thereafter be subjected to an oxidation to restore the dye, with which the textile has been impregnated; to the insoluble form.

The reduced or leuco solution of many va dyes has a. color distinctly different from the unreduceddye, and the normal color isrestored While generally satisfactory results have been. ,obtained by such oxidation treatment, the use stuff may with advantage'be effected by treatment. with sodium chlorite; The chlorite may be used in conjunction with an acid, for instance treatment with an oxidizing agent to bring out the use of, acid in the oxidation treatment-may alsobe avoided. V s

We have found that the oxidation of the dyethe acetic acid conventionally employed. However, we have found that the use of both dichromate and acid may with advantage be avoided by using as the oxidation bath an aqueous solution of sodium chlorite and a buffer salt such as sodium bicarbonate.

The reduced dyestufl' may be oxidized on the fabric in accordance with our invention by the use of the chlorite alone. However, we have found that, where the pH of the textile is reduced by the use of an acid or sodium bicarbonate or the like in conjunction with the chlorite, the oxidation proceeds more rapidly. Various acid salts or buffer salts suchas phosphates may be used for the purpose of lowering the pH but we have obtained particularly satisfactory results by usingsodium bicarbonate in conjunction withthe chlorite, as hereinafter more fully described.

- The invention is also applicable tothe aftertreatment of textile materials which have been dyed with a so-called sulphur dye. Some of the ing agents such as sodium sulphide and sodium of sodium dichromate and acid for this purpose has several disadvantages. In the first place, for

an adequate supply of dichromate, we are dependent upon importation'from distant war zones. Also, where dichromate is used, the oxidation treatment must be followed by a very thorough washingto avoid deleteriously affecting the shade of the dyed textile and prevent skin rash." The dichromate has a tendency to dull the shade of the textile and, if the oxidation temperature is ing treatment of vat dyes described above, inv

compound is formed in the cloth which cannot carbonate are customarily used. Though sulphur dyes may sometimes be used with no subsequent oxidation treatment, the textile impregnated therewith is usually treated with an aqueous oxidizing solution such as a solution of sodium dichromateand'acetic acid, similar to the oxidizorder to produce heavier shades and in improve the fastness of the dyed textile, especially its fastness to washing.

In general, our improved method of oxidizins ,vat dyes with which the textile is impregnated and the after-treatment of textiles dyed with sulphur dyes is substantially'the same, except that in the lattera slightly lower temperature is usually employed. It comprises treating the textile,

while impregnated with the dyestuif, andwhich may have been subjected to preliminary washing with an aqueous solution of sodium chlorite advantageously containing also sodium bicarbonate. In place of sodium bicarbonate, a weal: acid such as acetic acid or a phosphate buffer salt may be used as previously noted; The chlorite solution may also with advantage contain a operation will vary somewhat, depending upon special conditions but is readily determinable in the light of the present disclosure.

The dye-impregnated textile is ordinarily highly alkaline as it comes from the dye bath. As previously noted, we have found the chlorite oxidation of the dye to proceed more rapidly and.

to be generally more satisfactory, if the compo sition of the chlorite solution be such as to re- The optimum concen- I tration of chlorite to be used in any particular duce the alkalinity of the impregnated textile.

Particularly satisfactory results are usually obtained by maintaining the alkalinity of the bath within the range of about pH 8 to about pH 10.5. However, a pH from about 3 up to that approx imating the pH of caustic soda may be used.

' Though the oxidation of the dyestuiI may be effected by the chlorite in an acid solution this is not usually as desirable as a somewhat alkaline solution because of a tendency toward excessive generation of gases and danger of corrosion.

The reduction of alkalinity is advantageously effected, in accordance with our invention, by the inclusion in the chlorite solution of an amount of an alkalinity reducing substance adequate to produce the desired pH reduction. Sodium bicarbonate has been found particularly satisfactory for this purpose. Because of the characteristic pH of sodium bicarbonate, the alkalinity of the oxdizing solution is thereby readily maintained at an optimum pH value of about 8.3 or within the range of about pH 8 to about pH 10, and extra care to avoid using excessive quantities of the acidic constituent is unnecessary.

An oxidizing solution which we have found generally satisfactory for the aiter-treatment of either vat'or sulphur dyes may be prepared by dissolving about 1 pound of sodium chlorite and about 5 pounds of sodium bicarbonate in about 40 to 50 gallons of water.

A generally satisfactory oxidizing bath in which an acid is used in place of the bicarbonate may be prepared from the following ingredients and approximate proportions'thereof:

Water -gallons 250 Sodium chlorite pounds 2 Acetic acid (28%) do 10 Advantageously, about 3 ounces of tetrasodium pyrophosphate or a similar detergent material may also be added.

In the after-treatment of the vat dyes the temperature of the oxidation bath is advantageously maintained at about 140 F. In the aftertreatment of sulphur dyes it is usually desirable to maintain the bath at about 10 degrees lower temperature, In either case, somewhat higher or lower temperatures may be used. v

The treatment of the textile withthe chlorite solution may be eifected in the manner and by the apparatus ordinarily used in conventional practice. For instance, the textile may be passed through the chlorite oxidizing bath by means ofconventional jigs. Usually the textile is passed from one roller through the bath onto a second roller. 4 This operation may be repeated a number of times and each passage of the textile through the bath is designated an end. Prior to and following the chlorite treatment, the textile may be given several ends through wash water.

Advantageously, where sodium bicarbonate is used in conjunction with the sodium chlorite, half of the chlorite and all of the bicarbonate are dissolved in the bath. The textile is given one end through this bath and then the remainder of the chlorite added and the cloth given several additional ends through the bath.

The invention will be further. described by means of the following specific illustrations of its application:

Example I In the vat dyeing of a 1.69 yards per pound twill an olive drab shade, using a machine jig,

the fabric after having the dye padded thereon, in the conventional manner, was given three ends in a bath of hydrosulphite and caustic soda and then-transferred without washing to a second jig containing 50 gallons of water to which had been added one pound of sodium chlorite dissolved me half gallon of water, the temperature of the solution raised to F., and 1% gallons .of 28% acetic acid added. The'cloth was given three ends through this solutidn, each end requiring seven minutes, and was then washed and sent to the soaper. pH of the solution during the various stages of the operation were as follows:

Stage Avaollfible pH Percent Start... 0.28 4.3 After first end 0. 196 4. 3 After second end. 0. 045 4. 3 After third end 0. 045 4. 3

A complete oxidation of the dye was effected by this treatment.

Example II through this oxidizing solution at a temperature of 140 F., after which ittwas washed by four ends through cold water followed by two ends through hot water and passed toan ordinary soap solution containing one pound of soda ash.

The condition of the oxidizing bath during th operation'was as follows: 1

Available Stage Ch pH Percent Beginning first end 0. 280 4. 4 Middle first end..... 0.177 3. 8 Beginning second end 0. 112 4. 2 Beginning third end.. 0.074 4. 7 Beginning fourth end. 0.060 4. 7 Termination fourth end 0. 050 4. 8

The available chlorine and side.

Y assaisa Example III In two additional .runs, using an oxidation bath identical with that described in Example II, the cloth was given three ends through the chlorite bath instead of four, as in the preceding example. In the first of these runs, the cloth was given a cold water wash before soaping In the second of these runs, the cloth 7 down." was "soaped down directly after leaving the oxidizing bath with an ordinary soap solution to which two pounds of soda ash had been added. In these two additional runs, and in the run described as Example 11, the shade of the cloth was identical with that resulting from the dichroma'te oxidation ordinarily used.

From the runs of Examples Band III, itappears that, in accordance with our improved process wherein the oxidation is eflected by the A herringbone poplin of 1.60 yards per pound was padded with an O. D. vat dye and given eight ends through the conventional hydrosuiphitecaustic soda solution. 'I'hereafter, the cloth was Example V An approximately 600 gram package of twoply 's mercerized yarn was treated in an'experimental 'drum, package machine with an aqueous solution of hydrosulphite, caustic soda and synthetic detergent. A vat dye was then added and the solution in which the package was submergedwas circulated continuously for aboutminutes. The solution was, then withdrawn and a fresh solution of 68 grams of sodium bicarbonate in 6 quarts of water added. The temperature was raised to 140 F., and 3.4 grams of sodium chlorite added. After circulating this solution for 3 to 4 minutes, an additional 3.4 grams of sodium chlorite was added and the circulation continued for a total of about 15 minutes after the initial addition of the chlorite. The oxidizing solution was then withdrawn and the yarn washed twice in hotwater and once in warm water at a temperature of about 100 F., contain-- ing a conventional yam conditioner.

washed by two ends through cold running water and then subjected to oxidation and further washing. Using the conventional oxidation bath prepared from two pounds of sodium dlchromate and four quarts of 56% acetic acid, the oxidation required four ends and the subsequent washing, prior to soaping down, required four ends of the cloth through hotrunning water. In accordance with our improved method, by the use of an oxidation bath prepared from 1% to 2 pounds of.

Exam le v1 In a commercial operation in which an oxidation-bath of sodium chlorite and sodium bicarbonate was used, the process was carried out as follows, the fabric being heavy twill and herringbone of two yards per pound quality: The fabric from the dye bath was given fouren'ds through cold water and then passed to,the oxidizing bath in which a temperature of 140 F., was main' tained. The cloth was first given one end through the oxidizing bath containing five pounds of so- I dium bicarbonate and one-quarter pound of sodium chlorite in about 25 gallons of water. An additional one-quarter pound of sodium chlorite was then added and the cloth given three more ends through the oxidizing bath. Thereafter, it was given four ends through hot water at a temperature oi. about 180 F-.,-, followed by four ends rough a soap-sodium carbonate solution, three ends through hot water and shelled up through sodium chl'orite.and 2 quarts of 56% acetic -acid, complete oxidation was effected by only three ends through the bath, and the subsequent washing was effected by only one end through hot running water prior to soaping down instead of four runs required by the conventional method.

In each case the temperature of the oxidation bath was maintained at 140 F, The shade of the fabric treated by our improved method was identical with that resulting from the conven tional dlchromate oxidation.-

Inthe above run, only one pound of the chlorite was originally added. Half way through the first end the available chlorine had droppedto 0.08% and an additional to 1 pound of the chlorite was added at the beginning of the secondend. At the start of the flrstend, the 'pH of the chlorite solution was 3.5 and at-the te rmination of the third end it was 6.

In the preceding examples, the pH of the chlorite solution was maintained on the acid As we have previously noted, it is frequently desirable 'to use analkaline chlorite solution. This is readily accomplished bythe use of sodium bicarbonateor other salts capable of regulating the pH of the '-.solution,-in con- Junction with the chlorite. Examples of such use of bicarbonate are as follows:

' i and was thereafter shelled up through cold water;

and acetic acid.

cold water. The resultsobtained were substantially identical with those obtained by the same treatment of the fabric in the conventional manner, using an oxidizing bath of sodium dlchromate Example W I In dyeing a-challis type'fabric of 10 yards per pound spun rayon, the cloth was padded with an admixture of Indanthrene vat dye to give a green shade and the dyestufi thereon reduced by treatment for 20 minutes with an aqueous solution of sodium hydroxide and hydrosulphite in the conventional manner. Thereafter. the fabric was given two ends through wash waterand passed to an'oxidizing bath consisting of an aqueous solution of sodium chlorite and sodium bicarbonate. In the oxidizing treatment, the cloth was given one end through an aqueous bath to which 5- pounds of sodium bicarbonate and /a pound of sodium chlorite had been added. Thereafter, an

additional $4; pound of sodium chlorite was added to the bath and the cloth given three more ends therethrough. During this oxidationtreatment, which extended over a period of about 15 minutes, the temperature of the oxidation bath was maintained at F., and the pH thereof ranged from 8.3 to 8.45. Following the oxidation treatment,

the cloth was given two ends through hot water The results obtained by this treatment were highly satisfactory. The final washing was more readily effected than where conventional oxidizing methods are employed and there'was a. sub- 'stantial saving in the cost of chemicals. It is bonate used. The bicarbonate may be reduced by at least 50% without ill effects.

I have found, particularly where sodium bicarbonate is used in conjunction with the chlorite in my improved oxidation treatment, that material economy may be effected in the washing operations preceding and following the oxidation treatment without deleteriously afiecting the finished textile. Thus, in the operation described in the preceding Example VI, the washing following the oxidation and preceding the soaper may be reduced to two ends instead of four ends or this washing step may even be entirely eliminated without harmful effect on the finished cloth.

Also, because of the relatively mild but entirely efiective action of the chlorite and sodium bicarbonate constituents of my oxidation bath, the

textile may be passed directly from the dye bath to the oxidation bath without the usual intermediate washing. However, where this intermediate washing is omitted, more dyestufl and caustic i carried into the oxidation bath and, accordingly, more chlorite and sodium bicarbonate should be used. For example in the operation described in Example VI, where the preliminary washing is omitted, it is desirable to increase the amount of chlorite to about 1 /2 pounds and the amount of sodium bicarbonate to about 15 pounds. Under similar conditions, where the preliminary washing is not wholly omitted but is reduced to two ends instead of four'ends, about 1 pound of chlorite and about 12 pounds of sodium bicarbonate are usually sufficient. In either case, it is advantag'eous to add about one-half of the chlorite I to the oxidation bath prior to the first end and Example VIII A poplin of about 1.7 yards per pound, after impregnation with an admixture of sulphur dyestuff to give a brown shade, was passed without washing from the dyeing operation to a jig containing about 50 gallons of an aqueous solution to which had been added 1 pound of sodium chlorite dissolved in /2 gallon of water, the temperature of the solution raised to 130 F., and 1 gallons of. 28% acetic acid added. The cloth was given three ends through this solution and then washed and sent to the soaper. During the treatment with the chlorite solution, the temperature of the bath was maintained at 130 F. Entirely satisfactory results were obtained, the cloth being brightened and the wash-fastness of the dyed fabric substantially improved.

Example IX A heavy twill of 2 yards per pound quality, which had been impregnated with a sulphur dye to give a blue-green shade, was given 4 ends in cold water and thereafter subjected to treatment in an aqueous solution of sodium chlorite and sodium bicarbonate maintained at a temperature of 130 F. This'bath was prepared by adding to,

about gallons of water 5 pounds of sodium bicarbonate and A pound of sodium chlorite. The cloth was given one end through thisbath followed by three more ends through the bath after an additional pound of sodium chlorite had been added. The cloth was then given four ends through hot water and passed to the soaper.

As in the treatment of yet dyes previously discussed herein, the washing operations preceding and following the treatment with the sodium chlorite may be materially reduced from that of the preceding example, particularly where sodium bicarbonate is used in conjunction with the chlorite. Where my chlorite-bicarbonate bath is employed, the dye fabric may be passed direct- I 1y t0 the after-treatment with no intermediate washing or it may be given only two ends through the wash water. Following the chlorite treatment, the 'cloth may be passed immediately to the soaper or it may be subjected to a mild washing operation; say two ends through the wash water. However, some washing prior to the chlorite treatment is usually desirable 'as by such washing the amounts of chlorite and sodium bicarbonate required are reduced.

Where the textile being treated is of a nonabsorbent nature, it is desirable .to include in the oxidation bath a .pentrant to assist in the absorption of the oxidizing solution by the fabric.

We claim:

1. In the dyeing of cellulosic textile materials with a dyestuff of the class consisting of the sulphur dyes and the vat dyes which after application to the textile is subjected to an oxidation treatment to develop or improve its color and fastness, the improvement which. comprises effecting the oxidation of the dyestufi by treating the textile impregnated with the dyestuff with an aqueous solution of sodium chlorite, having a pH not less than about 3, for a period of time sufficient to effect the desired oxidation.

2. In the dyeing of cellulosic textile materials with a dyestuflf of the class consisting of the sulphur dyes and the vat dyes which after application to the textile is subjected to an oxidation treatment to develop or improve its color and fastness, the improvement which comprises effecting the oxidation of the dyestufi by treatin the textile impregnated with the dyestufi with an aqueous solution of sodium chlorite and an acid, having a pH not less than about 3, fora period of time sufiicient to efiect the desired oxidation.

3. In the dyeing of cellulosic textile materials with a dyestufl. of the class consisting of the SH]- phur dyes and the vat dyes which after application to the textile is subjected to an. oxidation treatment to develop or improve its color and fastness, the improvement which comprises effecting the oxiation of the dyestufl by treating the textile impregnated with the dy'estufi with an aqueous solution of sodium chlorite and acetic acid, having a pH not less than about 3, for a period of time sufficient to effect the desired oxidation.

4. In the dyeing of cellulosic textile materials with a dyestufl of the class consisting of the sulphur dyes and the vat'dyes which after application to the textile is subjected to an oxidation treatment to develop or improve its color and fastness, the improvementwhich comprises effecting the oxiation of the dyestuflf by treating the-textile impregnated with the dyestufl. with an aqueous solution of sodium chlorite and a buffer salt, having a pH not less than about 3, for a for a period of time sufficient to efiect the desired oxidation.

6. In the dyeing of cellulosic textile materials with a dyestufi of the class consisting of the sulphur dyes and the vat dyes which after application to the textile is subjected to an oxidation treatment to develop or improve its color and fastness, the improvement which comprises effecting the oxidation of the dyestuff by treating the textile impregnated with the dyestuff with an alkaline aqueous solution of sodium chlorite for a period of time suflicient to effect the desired oxidation.

7. In the dyeing of cellulosic textile materials with a dyestufl of the class consisting of the sulphur dyes and the vat dyes which after application to the textile is subjected to-an oxidation treatment to develop or improve its color and iastness, the improvement which comprises effecting the oxidation of the dyestuflf by treating the textile impregnated with the dyestufl with an aqueous solution of sodium chlorite for a period of time suflicient to effect the desired oxidation and maintaining the solution during the 1 treatment at a pH within the range from about.

8. Inthe dyeing of cellulosic textile materials with a dyestufi of the class consisting of the sulphur dyes and the vat dyes which after application to the textile is subjected to an oxidation treatment to develop or improve its color and Iastness, the'improvement which comprises efiecting the oxidation of the dyestui'! by treatingthe textile impregnated with the dyestufi with an aqueous solution of sodium chlorite for a period of time sufflcient to effect the desired oxidation and maintaining the solution during the treatment at a pH within the range from about 8-to 10.5 by the presence of sodium bicarbonate.

9. In the dyeing of cellulosic textile materials with a dyestufl of the class consisting of vat dyes and sulphur dyes which after application to the textile is subjected to an oxidation treatment to develop or improve its color and fastness, the improvement which comprises effecting the oxidation of the dyestuff by treating the textile impregnated with the dyestufl with an aqueous solution of sodium chlorite, having a pH within the range of about 8 to 10.5 and a temperature of about 130 to 140 F., for a period of time suflicient to efiect the desired oxidation.

10. In the dyeing of cellulosic textile materials 'with a dyestiifl. of the class consisting of. vat dyes and sulphur dyes which after application to the textile is subjected to an oxidation treatment to develop or improve its color and fastness, the improvement which comprises efiecting the oxidation of the dyestufl by treating the textile impregnated with the dyestufl with-an aqueous solution of sodium chlorite, containing about two pounds of sodium chlorite per one hundred gal lens of solution, at a temperature oiabout 130 to 140 F., for a period of time sufllc'ient to etfeet the desired oxidation and maintaining the pH of the solution within the range of about 8 to 10 by the presence of bicarbonate of soda.

GEORGE P. VINCENT. ARCHIE L. DUBEAU. 

